1. Field of the Invention
The present invention relates generally to the field of D-glucosamine hydrochloride, and more particularly to a method to prepare D-glucosamine hydrochloride using citric acid residue.
2. Description of Related Art
Citric acid is a widely used organic acid, and can be used as sour agent, thickening agent, or cleaning agent. It is commonly used in food, beverage, medical, chemical and detergent industries. Stimulated by export, the output of citric acid in China increased from 380,000 tons in 2001 to 700,000 tons in 2005, and nearly 800,000 tons in 2006. With an annual growth of 12.5%, China has become the biggest citric acid producing country, accounting for 70% of the global output. However, at present most manufacturers are still preparing citric acid in the method of fermentation, and during the process, vast amounts of citric acid residue are directly discharged without comprehensive utilization.
D-glucosamine hydrochloride (molecular formula: C6H13NO5.HCl), is a white crystal, odorless and slightly sweet, easily soluble in water, slightly soluble in methanol and insoluble in organic solvents like alcohol. D-glucosamine hydrochloride is a basic unit of many significant polysaccharides in biological cells, and is an important precursor to synthesize bifidus factors. Having many important physiological functions in an organism, it is mainly used clinically to enhance functions of the body's immune system, and to constrain overgrowth of cancer cells or fiber cells, offering functions of inhibiting and curing cancers and malignant tumors; it is also effective in curing various inflammations. Moreover, because glucosamine can prevent accumulation of cholesterol in the body, long-term usage of glucosamine can have a good anti-aging effect. At present, D-glucosamine hydrochloride is the newest 3rd-generation sanitarian functional food additive in tunicin health food series, and can be used as a food antioxidant, infant food additive, low caloric sweetener for diabetics, or a food additive to fight or prevent cancer, or lower blood fat and blood pressure; Meanwhile, D-glucosamine hydrochloride is also used in the medical industry, for example, as a biochemical reagent to synthesize medicines, or as an antibacterial and immune adjuvant. It is an activating agent for the body to fight influenza virus. D-glucosamine can also be used in food, cosmetics and feed additives, offering wide application fields.
At present, the traditional method to produce D-glucosamine hydrochloride is chitin preparation, i.e., firstly extracting chitin or chitosan from lobster or crab shells, and then obtaining D-glucosamine hydrochloride through hydrolysis with hydrochloride. This preparation method has the following main disadvantages:
Firstly, D-glucosamine hydrochloride extracted from shells of aquatic products is not suitable for patients allergic to aquatic products;
Secondly, the purification process is complicated, and the product has a fishy odor and is unstable;
Thirdly, due to pollution of ocean environment, D-glucosamine hydrochloride extracted from lobster and crab shells is inevitably subject to heavy metal pollution.
In order to overcome the shortcomings of the above production method, there has been some public patents prior to the present invention in relation to preparation of D-glucosamine hydrochloride from citric acid residue, such as China patent applications CN200810088877.5 and CN200810238484.8. However, inventors of these patents all have a mistaken concept that the volume concentration of hydrochloric acid and temperature of the hydrolysis reaction can not be too high at the same time, especially the temperature of the hydrolysis reaction shall not be over 90° C., otherwise it will cause carbonization of the citric acid residue, and consequently lead to lower output. On the other hand, when reaction takes place at a temperature lower than 90° C., the reaction time will be much longer. Generally, it takes more than 10 hours for each complete reaction, and therefore production efficiency is greatly reduced.